Seat post assembly for cycles

ABSTRACT

A vertically adjustable seat post assembly for cycles includes a light-weight vertical seat post formed from a relatively soft high strength-to-weight material, such as a carbon fiber composition, and a relatively hard tubular protective shim permanently secured concentrically about the lower end of the seat post. The outer diameter of the shim is slightly less than the inner diameter of the seat tube opening of the cycle frame, whereby the carbon fiber seat post is protected by the shim when the seat post is vertically adjusted and clamped within the seat tube opening.

FIELD OF THE INVENTION

[0001] This invention relates to a seat post assembly for cycles,including a seat post formed of carbon fiber or other relatively softhigh strength-to-weight material, and a protective tubular shim orsleeve formed of a hard metal material and arranged concentrically aboutthe lower end of the seat post, thereby protect the seat post againstdamage during the vertical adjustment thereof relative to the cycleframe.

BACKGROUND OF THE INVENTION Brief Description of the Prior Art

[0002] The use of lightweight componentry, such as a seat post, inbicycles, motorcycles, and other cycles is often seen as an opportunityto reduce the total weight in order to increase the efficiency of thecycle. However, since cycle components (i.e., a seat post) are reliedupon to support the weight of the rider, the strength of the componentcannot be compromised in order to reduce the weight of the part. As aresult, cycle component manufacturers have used advanced materials withhigh strength-to-weight ratios, such as carbon fiber, titanium,magnesium, beryllium and high strength aluminum, to produce lightweightcomponent parts. The state of design for light-weight cycles such asbicycles, though, depends upon the compatibility of the componentry towork on a wide variety of frame designs, and within various industrystandards in regards to size and specification. That being the case,component manufacturers are limited in their ability to optimize thecomponent design for the use of such advanced materials. In addition,many bicycles are assembled and serviced by untrained mechanics andconsumers who might compromise the structural integrity of a componentformed from advanced materials through improper installation.

[0003] Seat posts are particularly at risk of being compromised by thepreviously mentioned threats and limitations due to the describedfunction of the seat post. The necessary adjustability, compatibilitywith various frame designs, and the fact that the seat post supports thegreatest percentage of the rider's weight during travel make the use ofadvanced materials potentially dangerous should the seat post failduring use.

[0004] Over the years manufacturers have produced very lightweight seatposts (200 g or less for a seat post 300 mm or longer) with pillars madefrom carbon fiber, high strength aluminum alloys and titanium.Historically, in-the-field failures of these kinds of seat posts havebeen common. In addition to improper installation and abusive riding, acommon cause of seat post failure has been the irregular deformation ofthe clamping devices used to secure seat posts into the bicycle frame.The out-of-round shape that results from the clamping device beingsecured can create a stress riser on the seat post at the point where itenters the bicycle frame. This is also the point of the peak bendingmoment during the dynamic loading of the seat post in use. As a result,the ultimate strength of the part can be greatly reduced and broughtinto the range of typical service loads. This affect is even morecompromising in materials that are particularly notch sensitive, such ashigh strength aluminum and carbon fiber.

[0005] In order to counter the notch sensitivity of such materials manyseat post manufactures have turned to using internal reinforcements tothe seat post pillar either made from the same or different materials asthe pillar or integral to the seat post pillar itself. However, if thiskind of reinforcement is used over the entire length of the pillar, theweight advantage of using an advanced lightweight material may be lost;and if the reinforcement is used in only part of the pillar, there isthe possibility that the rider will adjust the pillar so that anon-reinforced portion of the pillar is subject to the stress risercreated by the clamping device.

[0006] Titec Cycle USA, Inc. developed a carbon fiber seat post called“the C-1 91 ”. Originally, it was believed that a carbon fiber compositepillar could be developed that would not require reinforcement.Nonetheless, the conclusion was arrived at that a sufficientlylightweight composite tube could not be developed that had adequate hoopstrength to withstand the stress riser created by the seat tube clampingdevice. As a result, the decision was made to install an extrudedaluminum alloy shim on the interior of the composite pillar in order toreinforce the tube in a limited clamping area defined by a graphic onthe outer diameter of the seat post pillar. This reinforcementeliminated most of field failures of the seat post, but not all. Manyconsumers would insert the seat post into their bicycle frame past thedesignated clamping area, where the post would fail under a substantialload.

[0007] Another manufacturer, Easton Sports, Inc., introduced the “CT2”carbon fiber seat post, which was integrally reinforced through the useof a variable wall thickness. This variable wall thickness design alsorequired that a limited clamping area be defined by a graphic on theouter diameter of the seat post. However, multiple field failures droveEaston to perform multiple product redesigns, which extended thereinforced area of the seat post pillar and increased the product'sweight. Additional field failures then lead to the incorporation of twoflats on the cross-sectional outer diameter of the seat post. Theseflats provided a relief from the stress riser created when the seat tubeclamping device deforms.

[0008] The U.S. patent to Ochoa U.S. Pat. No. 5,888,214 discloses theprovision of a compression device between a cycle frame and a cycleseat. A metal interacts with a compression rebound unit within a housingwhich is slidably inserted into the hollow cylindrical bicycle seat postmast and is secured in the mast with a set screw, thereby cushion theride of the user.

[0009] Carbon fiber composites can be optimized by their fiberorientation to withstand substantial loads, and providestrength-to-weight ratios superior to almost any other know materials.However, that optimization is best achieved when the fiber orientationis almost entirely unidirectional. If the seat post application requiresmulti-directional strength characteristics, then additional layers ofthe carbon fiber fabric maybe required in the lay-up in order to meetthe strength requirements and the weight advantage will be lost. Inaddition, since there is a range of seat post diameters that areconsidered standard, anywhere from 25.4 mm to 31.8 mm, it is difficultto optimize the lay-up for each size. It is also cost prohibitive tocreate tooling and to stock inventory for seat posts in each of thevarious standard sizes.

SUMMARY OF THE INVENTION

[0010] Accordingly, a primary object of the present invention is toprovide a seat post assembly for cycles, including a seat post having aprotective shim concentrically secured to the exterior of the lower endof the seat post, thereby to protect the seat post when inserted withinthe seat tube of a cycle frame. The shim further provides a mountingsurface for the seat post within the cycle frame to regulate the heightadjustment of the saddle height relative to the cycle frame to ensure asafe height adjustment. The shim is secured to the outer diameter of theseat post with the length of the shim being sufficient to accommodatethe normal range of adjustment required to fit the rider to theirbicycle, thereby leaving the remainder of the carbon fiber seat postexposed. The insertion of the seat post is limited by the length of theshim, since the outer diameter of the carbon fiber seat post is smallerthan could be secured by the bicycle frame's clamping device.

[0011] By using the outer diameter of the shim to mate to the interiordiameter of the seat tube of the frame, the carbon fiber seat post andsaddle clamp assembly parts could be common in the production of seatposts in each of the twelve industry standard sizes. Only the outerdiameter of the shim would have to be changed, and the shims could beeasily machined from one or two extrusion sizes.

[0012] The reduced diameter necessary for the carbon fiber seat post tofit within the common interior diameter of the shim makes the seat postmore flexible. This added flexibility, in conjunction with naturaldamping characteristics of the carbon fiber material, reduce thevibration and shock normally transmitted to the rider through the seatpost and produce a more comfortable ride. The reduced fatigue on therider allows him to perform at a higher level of efficiency over alonger period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Other objects and advantages of the invention will becomeapparent from a study of the following specification when viewed in thelight of the accompanying drawings, in which:

[0014]FIG. 1 is a perspective view of the seat post, shim, and saddlemeans;

[0015]FIG. 2 is a perspective view of the assembled cycle frame, clampmeans, seat post means and saddle means;

[0016]FIG. 3 is a side view of the cycle frame, clamp means, seat postmeans, and saddle means;

[0017]FIG. 4 is a longitudinal sectional view of the cycle frame, clampmeans, seat post means, and saddle means of FIG. 3;

[0018]FIG. 5 is a top sectional view of the clamp means and cycle frametaken along line 5-5 of FIG. 3;

[0019]FIG. 6 is a sectional view of the cap portion of the saddle means;

[0020]FIG. 7 is a partially sectioned elevational view of the seat post;

[0021]FIG. 8 is an elevational view of the shim; and

[0022]FIG. 9 is a longitudinal sectional view of the shim.

DETAILED DESCRIPTION

[0023] Referring first more particularly to FIG. 1, the seat post means2 of the present invention includes a tubular seat post 4, and a tubularshim 6 mounted concentrically about the lower end of the seat post 4. Atits upper end, the seat post supports seat saddle means 8 having atubular cap portion 10 that is mounted concentrically about the upperend of the seat post 4. As will be set forth in greater detail below,the sleeve 6 and the cap portion 10 of the saddle means 8 arepermanently secured (i.e., are preferably adhesively bonded) to the seatpost 4.

[0024] Referring now to FIG. 2, a conventional cycle frame 12 forbicycles or motorcycles includes an tubular seat tube portion 12 a thatcontains a longitudinally extending slot 14, as best shown in FIG. 5.The opening in the upper end of the seat portion 12 a has an internaldiameter D₁ that is slightly greater than the outer diameter D₂ of theshim 6, thereby to permit insertion of the shim portion 6 of the seatmeans 2 within the seat tube opening 16, as best shown in FIG. 2.Conventional clamp means 18 are provided for compressing together thebifurcated portions of the longitudinally slit seat tube portion of theframe, thereby to clamp the seat post means 2 to the frame as is knownin the art. The saddle means 8 serves to support the cycle seat 20 asshown in phantom in FIG. 2.

[0025] Referring now to FIGS. 3 and 4, it will be seen that the seatpost means 2 is adapted for vertical adjustment relative to the seattube portion 12 a of the frame when the clamp means is in its releasedcondition, as will be described below. During this vertical adjustmentof the seat post means 2 relative to the seat tube portion 12 a, theshim 6 is always opposite the clamp means 18. In accordance with animportant feature of the invention, the clamp means 18 is operable toradially inwardly compress the bifurcated seat tube portion of the framefrom its normal diameter D₁ to a reduced constricted diameter incompressed engagement with the outer circumferential surface of the shim6. The diameter D₃ of the seat post 4 is, however, less than theconstricted reduced diameter of the seat tube, whereby the seat post 4will never be engaged by, or damaged by, the clamp means 18 and theassociated bifurcated portion 12 a of the frame seat tube.

[0026] Referring now to FIG. 5, the clamping means 18 includes abifurcated sleeve 22 having a pair of arm portions 22 a that aretraversed by a transverse bore that receives the clamping bolt 24. Atone end, the clamping bolt 27 includes a threadably connected knob 26,and at the other end, the bolt 24 is pivotally connected by pivot 26with a conventional operating cam lever 28. The cam lever 28 includes acam portion 28 a for displacing together the bifurcated arm portions 22a of the clamping sleeve 22, thereby to radially inwardly compress theseat tube portion 12 a to its constricted condition of reduced diameter.

[0027] As shown in FIG. 6, the lower end of the cap portion 10 of thesaddle means 8 is tubular and is open at its lower end for receiving thetubular upper end of the seat post 4. The cap portion 10 contains accessports 30 for introducing adhesive in the fluid condition into the spacebetween the interior of the cap portion 10 and the outer peripheralsurface of the seat post 4.

[0028] Referring now to FIG. 7, the tubular seat post 4 is formed of amaterial having a high strength-to-weight ratio, such as carbon fiber,titanium, magnesium, beryllium, and high strength aluminum, thereby toafford high structural strength with a relatively low weight.Preferably, the tubular seat post 4 is formed of a carbon fibercomposite material, wherein carbon fibers are bonded by an appropriateresin.

[0029] Referring now to FIGS. 8 and 9, the shim 6 is formed of a hardmaterial of relatively high strength, such as a 7000 series aluminumalloy, which contain more than 3 percent, but less than 10 percent zinc.According to one embodiment of the invention, a 7075 aluminum alloy wasused that contains about 2.5 percent magnesium, about 1.6 percentcopper, about 0.3% chromium, and about 5.6 percent zinc. The aluminumshim is preferably hardened by heat treatment and furnace aging. In theillustrated embodiment, the shim has a length of about 170 millimeters,and the seat post has a length of about 350 millimeters. Thus, thelength of the shim is about one-half of the length of the seat post,with the shim being arranged at the lower most extremity of the seatpost. Thus, the upper end of the seat post has a certain degree oflateral flexibility, thereby improving the support of the seat 20 andthe rider relative to the frame. Furthermore, the length of the shim isno less than 2.5 times the diameter of the seat post, in accordance withthe requirements of the Consumer Product Safety Commission. This meansthat a mark must be made between 69 to 79 millimeters from the bottom ofthe seat post, depending on the diameter, to define the minimuminsertion point of the shim within the opening 16 of the seat tube 12 a.This effectively limits the range of height adjustment of the seat postto the remaining 91 to 101 millimeters of the shim.

[0030] The carbon fiber material from which the seat post is formedcomprises a plurality of layers of carbon fiber fabric pre-impregnatedwith a binding resin, such as an epoxy resin, is commonly referred to as“pre-preg.” The orientation of the fibers in each layer are optimized toachieve the strength characteristics desired in the resulting structure.The specific orientation and/or number of layers of this sort is commonknowledge to those skilled in the art. This formation of layers—or“lay-up”—is then wrapped around a form—or mandrel—which is then eitherplaced inside a mold or fed into a die. In either case, the lay-up isthen heated within the mold or die to a pont at which then resin withinthe carbon fabric liquefies. Continued heating of the lay-up then causesthe resin to harden so that the lay-up assumes a permanent form s thenegative of the mold. As a whole, the process is referred to asthermoset carbon fiber molding.

[0031] While in accordance with the provisions of the Patent Statutesthe preferred forms and embodiments of the invention have beenillustrated and described, it will be apparent to those skilled in theart that various changes may be made in the invention without itdeviating from the inventive concepts set forth above.

What is claimed is:
 1. A seat post assembly for cycles, comprising: (a)a cycle frame having a generally vertical seat tube having an upper endportion containing an opening normally having an expanded conditionhaving a first inner diameter (D₁); (b) seat post means, including: (1)a vertical elongated seat post having upper and lower ends; and (2) atubular shim arranged concentrically about, and permanently fastened to,the lower end of said seat post, the length of said shim being less thanthe length of said seat post, the outer diameter (D₂) of said shim beingslightly less than said first diameter; (3) said seat post means beinginserted within said seat tube with said shim being arranged within saidseat tube upper portion; and (c) first clamp means for compressing saidseat tube upper portion radially inwardly toward a constricted conditionin clamping engagement with said shim, thereby to clamp said seat postwithin said seat tube.
 2. A seat post assembly as defined in claim 1,wherein said seat post is adhesively bonded to said shim.
 3. A seat postassembly as defined in claim 2, and further including: (d) seat meanssupported by said seat post upper end, said seat means including: (1) aseat; and (2) saddle clamp means supporting said seat, said saddle clampmeans including a downwardly extending tubular cap portion having anopen lower end, said cap portion lower end being concentrically mountedon, and permanently secured to, said seat post upper end.
 4. A seat postassembly as defined in claim 3, wherein said tubular cap portion isadhesively bonded to said seat post.
 5. A seat post assembly as definedin claim 4, wherein said shim and said tubular cap portion each containa plurality of access openings, thereby to permit the introduction of anadhesive in the fluid state into the spaces between said seat post andsaid shim, and between said seat post and said tubular cap portion,respectively.
 6. A seat post assembly as defined in claim 5, whereinsaid adhesive is a curable two-part epoxy resin.
 7. A seat post assemblyas defined in claim 2, wherein said seat post is tubular and contains anunobstructed through bore.
 8. A seat post assembly as defined in claim2, wherein said seat post has an outer diameter (D₃) that is less thanthe inner diameter of said seat tube when said seat tube is in saidconstricted condition.
 9. A seat post assembly as defined in claim 8,wherein the length of said shim is at least 2.5 times said seat postouter diameter (D₃).
 10. A seat post assembly as defined in claim 8,wherein said shim is formed from an aluminum alloy.
 11. A seat postassembly as defined in claim 10, wherein said aluminum alloy comprisesabout 2.5% magnesium, about 1.6% copper, about 0.3% chromium, and about5.6% zinc.
 12. A seat post assembly as defined in claim 11, wherein saidseat post is formed from a light-weight material selected from the groupconsisting of titanium, magnesium, beryllium, high strength aluminum,and a carbon fiber composite material.
 13. A seat post material asdefined in claim 11, wherein said seat post is formed from a carbonfiber composite material.
 14. A seat post assembly as defined in claim13, wherein the length of said shim is about one-half the length of saidseat post.
 15. A seat post assembly as defined in claim 13, wherein thelength of said shim is at least 2.5 times said seat post outer diameter(D₃), and further wherein the length of said seat post is about 2 timesthe length of said shim.
 16. A seat post assembly as defined in claim15, wherein said seat post is tubular and contains an unobstructedthrough bore.
 17. A seat post assembly as defined in claim 16, whereinsaid upper end of said frame seat tube portion contains a longitudinalslot.